Fertilization - In all animals, germ cells produce by meiosis eggs or sperm. Necessary for understanding the early evolution of animals.Ī. Transformation of a fertilized egg to a new individual. Reproduction, digestion, etc.) we have the grade of organization seen in all animals thatĮmbryology is the study of the progressive growth and differentiation that occurs during the When organs work together to perform some function (circulation, respiration, Organs appear first in the Platyhelminthese (flatworms). The aggregation of different kinds of tissues into organs is a further advancement in theĮvolution of animals. CnidariansĪre usually considered to be at this level of organization. Sponges are at this level ofĬells all of one type begin to function in a unified way to accomplish a task. Such cells do not become organized into true tissuesīut may form definite patterns or layers. Aĭivision of labor is evident, so that some cells are concerned with, for example, Protoplasm is differentiated into organelles capable of carrying out specialized functions.Ĭellular organization is an aggregation of cells that are functionally differentiated. Units that make up tissues, Tissues are the units that make up organs, and Organs make up organĮach level is more complex than the one before and, as a general rule, a more recent evolutionaryĪll life functions are confined within the boundaries of a single cell. Molecules are the units of organelles, Organelles are the units that make up cells, Cells are the In the evolution of animals so that there is considerable specialization and division of labor withinīody tissues.Some of the trends seen in animal evolution are:Īn animal (or a plant for that matter) is composed of many units organized into successive units: In animal evolution, structural complexity has increased Early Animals The Evolution of Early Animal Complexity
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